A hybrid vehicle comprises an internal combustion thermal engine, which transmits torque to the driving wheels by means of a transmission provided with a gearbox coupled with a clutch, and at least one electric machine, which is electrically connected to an electric accumulation system, and mechanically connected to the driving wheels.
The following is possible while traveling: either a thermal operating mode, in which the torque is generated only by the thermal engine and the electric machine may work as generator for recharging the electric accumulation system; or an electric operating mode, in which the thermal engine is off and the torque is generated only by the electric machine working as motor; or a combined operating mode, in which the torque is generated both by the thermal engine and by the electric machine working as motor. Furthermore, in order to increase overall energy efficiency during all steps of decelerating, the electric machine may be used as generator for a regenerative deceleration in which the kinetic energy possessed by the vehicle is partially converted into electric energy, which is stored in the electric accumulation system instead of being fully dissipated in frictions.
On some hybrid vehicles, the gearbox comprises a circulation pump for circulating lubricating oil through the gears of the gearbox so as to ensure adequate lubrication of the gears themselves. Furthermore, in the case of a hydraulically actuated automatic manual transmission (commonly named “AMT”), the gearbox further comprises an actuation pump which supplies the hydraulic pressure needed for hydraulic gear engagement and selection and clutch operation.
In the currently manufactured gearboxes, the gearbox pumps are actuated by an auxiliary activating shaft, which takes motion from the drive shaft (possibly with the interposition of a transmission shaft), i.e. upstream of the clutch, so that it is always actuated when the clutch is open. This condition makes the mechanical connection of an electric machine to a shaft of the gearbox less convenient, because in case of electric traction (i.e. when the thermal engine is off), the clutch must remain closed to actuate the pumps and therefore the thermal engine is also rotably fed (with considerable frictions and inertia). Furthermore, because the electric machine cannot be rotated when disconnected from the thermal engine (in these conditions there would be no lubrication of the gearbox and, above all, no hydraulic pressure needed to actuate the clutch), the electric machine cannot be used as starter motor of the thermal engine, because in order to use the electric machine as starter motor of thermal engine the electric machine must be rotated at high speed before connecting the electric machine to the thermal engine in order to make the electric machine accumulate a high amount of kinetic energy.
In order to solve the problem described above, it has been suggested to make the activating shaft of the pumps of the gearbox mechanically independent from the drive shaft, and to actuate the pump activating shaft by means of a dedicated motor; however, this solution normally requires re-designing the gearbox, with high development costs and little efficiency from the energy point of view, because when the thermal engine is running (i.e. for most time of use of the vehicle), it is more efficient to use part of the torque generated by the thermal engine to directly actuate the auxiliaries rather than converting part of the torque generated by the thermal engine into electricity, which is transformed back into mechanical torque by an electric motor. Furthermore, arranging an electric motor mechanically coupled to the activating shaft of the gearbox pumps is not easy, because the space in the gearbox area is small, it is rather hot by effect of the heat generated by friction inside the clutch and the gearbox, and is not very ventilated because it is normally in the middle of the vehicle.
Patent application US2008087487A1 describes a transmission for a road vehicle with hybrid propulsion comprising: a double clutch gearbox provided with two primary shafts, a secondary shaft, and a lubrication pump; two clutches connected to the primary shafts and comprising a normally conductive part, which can be connected to a drive shaft of a thermal engine; and a reversible electric machine comprising a shaft mechanically connectable to one of the two primary shafts; a first mechanical transmission, which transmits motion from the normally conductive part of the clutch to the lubrication pump and comprises a first freewheel; and second mechanical transmission which transmits motion from the shaft of the electric machine to the lubrication pump and comprises a second freewheel.